Pills found at Prince‘s Paisley Park home in Minnesota were counterfeit drugs containing fentanyl – a synthetic opioid said to be 50 times more powerful than heroin.

An official close to the investigation anonymously told The Associated Press that the pills were found in bottles falsely mislabelled as ‘Watson 385’ – a term used to identify pills containing acetaminophen and hydrocone.

Majority of the pills were found in bottles of Vitamin C and aspirin found in suitcases and bags while some were also found in his dressing room at Paisley Park.

Medical officials confirmed in June that Prince died from an accidental fentanyl overdose.

As the pills Prince was taking were counterfeit there is speculation that Prince was unaware that there was fentanyl in the pills. As The Guardian reports, users often don’t know they are taking fentanyl which increases the likelihood of overdose.

While it’s unknown whether Prince knew he was taking fentanyl or not, tests done on the singer before his death did not show any fentanyl in his system making it likely that he was not a longtime user. The official said he probably took the fatal dose in the 24 hours before he died.

The official further said that Prince had no prescription for any controlled substances in the state of Minnesota in the 12 months before he died. Authorities are reportedly still investigating how Prince got a hold of the drugs.